Isolation of a bent dysprosium bis(amide) single-molecule magnet

The isolation of formally two-coordinate lanthanide (Ln) complexes is synthetically challenging, due to predominantly ionic Ln bonding regimes favoring high coordination numbers. In 2015, it was predicted that a near-linear dysprosium bis(amide) cation [Dy{N(Si ⁱPr ₃) ₂} ₂] ⁺ could provide a single-molecule magnet (SMM) with an energy barrier to magnetic reversal (U _eff) of up to 2600 K, a 3-fold increase of the record U _eff for a Dy SMM at the time; this work showed a potential route to SMMs that can provide high-density data storage at higher temperatures. However, synthetic routes to a Dy complex containing only two monodentate ligands have not previously been realized. Here, we report the synthesis of the target bent dysprosium bis(amide) complex, [Dy{N(Si ⁱPr ₃) ₂} ₂][Al{OC(CF ₃) ₃} ₄] (1-Dy), together with the diamagnetic yttrium analogue. We find U _eff = 950 ± 30 K for 1-Dy, which is much lower than the predicted values for idealized linear two-coordinate Dy(III) cations. Ab initio calculations of the static electronic structure disagree with the experimentally determined height of the U _eff barrier, thus magnetic relaxation is faster than expected based on magnetic anisotropy alone. We propose that this is due to enhanced spin-phonon coupling arising from the flexibility of the Dy coordination sphere, in accord with ligand vibrations being of equal importance to magnetic anisotropy in the design of high-temperature SMMs.